Tunneling with OpenSSH

SSH Tunneling or SSH port forwarding is typically useful if you have a network with a private segment like this:

                                                                 -----------------------------------------------------------
                                                                |                                                           |
                                                                |                                                           |
                 ---------                                -----------                    --------------                     |
                |localhost|------------------------------|   gateway |------------------|  hidden      |                    |
                 ---------                               | 10.2.2.18 |                  | 172.16.0.42  |                    |
                                                          -----------                    --------------                     |
                                                                |                                                           |
                                                                 -----------------------------------------------------------

On localhost forward port 2222 to hidden's port 22:

ssh -L 2222:172.16.0.42:22 gateway

Then you can e.g. scp from localhost to hidden by using localhost's port 2222:

scp -P 2222 file1 localhost:

See also

• set up NAT